1. Field of the Invention
The present invention relates to a process for depositing transparent, non-metallic, functional intermediate layers using selected starting compounds between two films in an, as such, known manner in vacuum, as well as to a composite film produced with this process.
2. Description of the Related Art
Composite films composed of two films and a bonding layer having specific functions are known. There are composite films which have an intermediate functional layer which is permeable to light and simultaneously acts as a barrier, i.e., a gas-permeability-diminishing barrier layer. Other intermediate functional layers are known which are permeable to light but which are simultaneously provided with electrically conductive layers.
Intermediate functional layers have also been fabricated which are layers which are transparent in the visible radiation range but which reflect infrared radiation.
Various processes are utilized for the fabrication of film composites of this type.
The most commonly applied processes include coextrusion, (co-) extrusion coating, extrusion lamination, and lining film formation wherein two sheets of film are joined with the aid of an adhesive.
Films having vacuum deposited functional layers of, e.g., aluminum or SiO.sub.x, as a barrier layer for gases or aromatic materials are made nearly exclusively into composites by lining film formation. Depositing a second film yields good composite sealing properties and simultaneously the very sensitive, vacuum evaporated layers are protected against mechanical stress or environmental influences, because the thin functional layer is embedded between two thicker films.
So-called "vapor deposited" films require extremely careful handling both during production and subsequent processing, because even only a little mechanical stress distinctly impairs the barrier properties of such films.
For environmental purposes, products are designed today in such a manner that they can be recycled after use. This is especially the case with packaging materials. From this aspect, composites present a big problem due to the many different materials involved. For this reason, an attempt has been made to use base film materials which are as uniform as possible and therefore to permit better joint recycling. Thus, for example, pure polyolefin composites having a SiO.sub.x barrier layer are known. In order to fabricate a composite of this type, however, it is presently necessary to use lining adhesives which develop an unmeltable lattice after hardening. This lattice makes recycling difficult.
In order to achieve improved environmental compatibility, an attempt has been also made to develop biologically degradable and compostable packaging materials. The chief disadvantage of the presently-available biodegradable plastics is their poor barrier properties, in particular, for water vapor. For this reason, an attempt has been made to improve the barrier properties by employing a vacuum coating. Like conventional "vapor deposited" films, "vapor deposited" biodegradable films are extremely sensitive to mechanical stress encountered during fabrication and subsequent processing impairing the integrity of the barrier. The vacuum evaporated layers, therefore, have to be embedded, such as, between two films, varnished, etc., to protect them. In order to obtain good sealing properties, moreover, it is necessary to deposit a sealing layer on the vapor deposited biodegradable films. As in conventional composites, this can be accomplished with lining technology. The lining adhesives employed for this are, however, not biodegradable and, thus, are not compostable like the vapor deposited films and the sealing layer. Thus, they may interfere with compostation.
In order to save energy, coated architectural glass is frequently employed today. Depositing thin layers in a vacuum can yield coated glass panes with high thermal insulation properties and/or sun-protection properties. Films are coated for the same reason and can be deposited onto the glass panes. Films of this type are coated on one side, that is, the functional layer lies, for example, exposed on the glass prior to lining and can, therefore, easily be damaged, mechanically or in view of their sensitivity to environmental influences, e.g., a silver coating which is sensitive to chlorine- or sulfur-containing compounds.
For electro-optical components, such as liquid crystal displays, electrically conductive coatings which are transparent to visible light are utilized, for example, on glass or plastic. In this case, too, the deposited layer is exposed and can be easily damaged during subsequent processing.
A composite film is known from GB 2 064 427 A. Although it is produced without a lining adhesive, the resulting functional intermediate layer is, however, vapor deposited, which prevents oxidation of the metal surface prior to adhesion developing due to its getter effect. The result, however, is the production of composite films which do not have a transparent barrier layer.
All composite films having transparent intermediate functional layers to date, therefore, have the disadvantage that they are produced using a lining adhesive and, consequently, cannot be easily recycled or cannot be recycled at all, as well as having to accept the additional drawback of even more greatly diminished barrier properties.
The composite films fabricated according to GB 2 064 427 A have an intermediate functional layer deposited without a lining adhesive, however, this intermediate functional layer has the decisive drawback that it is metallic and not transparent and therefore cannot be used for the just-described applications.
On the basis of this, it is an object of the present invention to provide a process with which composite films can be produced without employing a lining adhesive, while simultaneously demanding that there are no restrictions regarding the function of the layer.